The objective of the project is to study the heterogeneity of human growth hormone by characterizing chemically, biologically and immunologically the nine components that constitute preparations of the hormone. The components, all of which have been detected in radioimmunoassay quality preparations, are listed together with the amounts generally present in preparations. 1. Disulfide dimer 2-10%. 2. 20,000-dalton structural variant 2-10. 3. Diabetogenic factor less than 1. 4. Slow GH (highly lactogenic GH) 5-10. 5. Slow, slow GH (only recently isolated) 2-5. 6. Enzymically cleaved forms 5-10. 7. Deamidated forms 5-10. 8. Fast GH (only recently detected) 5-10. 9. Major component 50-60. The proteins will be studied by four electrophoresis methods, peptide mapping, amino acid sequencing, bioassays (rat and pigeon), liver and mammary gland receptor assays, radioimmunoassays, in vitro assays for activities in fat, protein and carbohydrate metabolism. Four of the forms (20K, slow-GH, slow slow-GH and fast-GH) are new pituitary hormones only recently recognized as being unique substances.